Problem: Expand. If necessary, combine like terms. $(5x+1)(5x-1)=$
Answer: Notice that this expression has the following special form: $(a+b)(a-b)$ This form expands to what we call "a difference of squares": $( a+ b)( a- b)= a^2- b^2$ Using the above pattern, we get: $\begin{aligned} ({5x}+ 1)({5x}- 1)&=({5x})^2- 1^2 \\\\ &=25x^2-1 \end{aligned}$